Many environmentally prevalent chemicals have or are suspected of having effects on estrogen (i.e., kepone, DDT, PCBs). The presence of estrogen at a critical period during development is believed to be necessary for the differentiation of sexual, morphological, and functional characteristics. It is suspected that environmental toxicants might influence sexually dimorphic behaviors by interfering with the presence of estrogen during this critical phase. The purpose of this research is to: (1) develop an animal model to assess effects on sexual differentiation using chemicals such as estrogen and testosterone that have known effects on sexually dimorphic characteristics and (2) employ the model to study environmental toxicants with potential estrogenic activity. Reproductive-based sexual behaviors, nonreproductive sexually dimorphic behaviors, and organ weights will be used in these experiments; sexually dimorphic liver enzyme function will also be studied.